(57bp) Experimental Study on the Characterisation of Flammability of Methane Enriched in Hydrogen in the Framework of Risk Assessment of Injection of Hydrogen in Natural Gas Network (concept "POWER TO GAS")

In the context of planning a decarburization of the European Union energy sector, in order to reach a reduction of carbon emissions up to 95 % by 2050, several studies on the compatibility of the existing gas networks with blends of natural gas enriched with hydrogen up to 20% of hydrogen have been tested in industrial scale projects.

The explosion process of multi-component gas mixture is extremely complex and may cause serious disaster effects. The safety issue concerning explosion of multi-component gas mixture is urgent to be investigated on account of its wide range of applications. In current work, series of experiments to characterize severals parameters (Lower Explosive Limit - Upper Explosive Limit - Lower Oxygen Concentration - Maximum Pression - Gas explosion constant - Minimum Ignition Current - Maximum Experimental Safe Gap - Ignition Sensitivity) were performed in a 20 L spherical explosion vessel at initial conditions of 1 atm and 293 K, involving methane-hydrogen/air mixtures.

In relationship to the European Union ATEX Directive 2014/34/EU and protective systems intended for the use in potentially explosive atmospheres, gases and dusts are classified according to their ignition properties. The explosion group for gases and vapors is determined by the maximum experimental safe gap (MESG) and/or minimum ignition current (MIC) ratio values, both defined in the ISO/IEC 80079 (Explosive Atmosphere—Part 20-1: Material characteristics for gas and vapour classification—Test methods and data) standard.

This paper presents the experimental results produced by Ineris highlighting the influence of the addition of hydrogen on the flammability and explosive properties of the natural gas-hydrogen mixture (0-20% Vol.).

The presence of hydrogen has a negligible influence on certain properties such as:

o the lower explosive limit,

o the oxygen limit concentration,

o the maximum explosion pressure,

o the self-ignition temperature;

The following properties are more sensitive to hydrogen content:

o the upper limit of explosiveness increases linearly with the hydrogen content in methane;

o Industrial methane, like natural gas, is classified in Group IIA on the grounds that it contains no more than 25% Vol. hydrogen. A mixture of methane with other compounds of group IIA of any proportion is classified in Group IIA;

o the maximum pressure-mounting speed remains constant and equal to that of methane up to about 15 % hydrogen, but increases rapidly for higher hydrogen levels;

o the minimum ignition energy decreases rapidly as the hydrogen content increases, suggesting an increase in the probability of inflammation with the hydrogen content (which, however, has yet to be confirmed by specific tests). However, for low hydrogen levels (10% max), the probability of ignition, although greater than for natural gas alone, would remain in the same orders of magnitude.